Optical circulators are used in fiber optic networks to switch signals between different optical fiber cores. An optical circulator is a non-reciprocal device that circulates the propagation of light in one direction among multiple input/output optical ports, with any two consecutive optical ports operating as optical isolators. For example, light from a first optical port is propagated to a second optical port, while light propagation in a reverse direction from the second optical port back to the first optical port is inhibited. Light from the second optical port is propagated to the next port in the series. As such, the second optical port operates as both an input port (receiving light from the first optical port) and an output port (transmitting light to the next optical port).
A reflective optical circulator is a particular type of circulator that uses a mirror opposite the light port end of the circulator to reflect light between optical ports, thereby reducing the number of optical components and, thus, the size of the optical circulator. Between the mirror and the optical ports are optical components to separate, rotate, and combine orthogonally polarized light beams in order to couple light among selected pairs of optical fibers attached to the circulator's optical ports. The optical fibers used in these networks typically consist of a core surrounded by a cladding, and one or more layers of protective coatings. Core diameters are typically in the range of 5 to 10 .mu.m with an outside fiber diameter of 125 .mu.m.
One disadvantage with some prior art circulators is that they do not circulate light from the last optical port to other optical ports in the series. As such, the last optical port is limited to use as only an output port, thereby limiting the capacity of the circulator.
Another disadvantage with some prior art optical circulators is that the large size of the optical fibers typically coupled to these circulators necessitates the use of larger optical components to circulate light among the optical ports. In addition, the use of these large optical fibers may require the use of lenses within the optical ports to focus light from the optical fiber cores onto the circulator. These lenses also add to the size of the optical circulator. A large optical circulator, due to the use of larger or additional components, may not be desirable.